Compressor, including unloading head



Dec. 6, 1955 K. K. COOPER ETAL COMPRESSOR, INCLUDING UNLOADING HEAD Filed April '7, 1954 an L .m Y E E O B N T B R N U O WMQD T m N HS- TE m EL E NR H NA T EH KC Y B NM 0 0: N UE United States Patent 2,726,032 COMPRESSOR, INCLUDING UNLoADiNG Kenneth K. Cooper, North Caldwell, and Charles A. filthberley, Mountain Lakes, N. 1., assignors to General Electric Company, a corporation of New York Application April 7, 1954, Serial No. 421,558

7 Claims. (Cl. 230--22) The present invention relates to a compressor including an unloading head. More specifically the invention relates to an unloading head by means of which one or more cylinders of a multi-cylinder refrigerant compressor can be unloaded.

For the purpose of preventing overload on the compressor driving means or for the purpose of controlling the output of a multi-cylinder compressor unit, it is desirable to provide some means for unloading one or more compressor cylinders under certain conditions of operation. Most compressor unloading arrangements include either pressure operated valves in the discharge line from the compressor cylinder or comprise some means for holding either the suction valve or the exhaust valve open during the entire piston stroke. Such unloading arrangements involve a number of vdisadvantages. With unloading arrangements provided in the discharge line from the compressor the compressor valves continue to function even when the compressor cylinder is unloaded with resultant valve and power losses. Arrangements in which the exhaust or inlet valves are held in an open position for unloading the compressor cylinder are usually quite complex and expensive and are not particularly adaptable to use with hermetically sealed compressor units. I

It is an object of the present invention to provide an unloading head for a compressor cylinder which is of simple construction and which includes a minimum number of operating elements.

It is a further object of the present invention to provide an unloader head for the compressor cylinder which bypasses the compressor valves in unloading the cylinder directly to suction pressure. 7

Another object of the invention is to provide a compressor unloading head requiring a minimum amount of power for the operation thereof.

A further object of the invention is to provide a compressor including an unloading arrangement which circulates cooling suction gas through the unloaded cylinder during operation thereof in the unloaded state.

Further objects and advantages of the invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In carrying out the objects of the present invention, there is provided a gas compressor including a compressor cylinder, unloading head, a control cylinder, an unloader port and a piston disposed in the control cylinder adapted to close the unloader'port for normal operation of the compressor cylinder and for opening the port for unloaded operation of the compressor cylinder. j Means are also provided for admitting fluid to the control cylinder at sufiicient pressure to maintain the piston in a position which closes the unload er port during normal operation of the compressor cylinder.

In the specific modification illustrated a' differential i piston'is, employed in the control cylinder and is main- 2,726,032 Patented Dec. 6, 1955 as compare'dwitlitlie suction gas pressure within the control cylinder effects movement of the differential piston to a position wherein the unloader port is opened to provide direct communication between the interior of the compressor cylinder and the source of suction gas. Dampening or cushioning means are also provided which tends to hold the diiferential piston in an unloading position to prevent chatter thereof during unloaded operation of the compressor and to cushion the piston as it moves into position closing the unloading port when discharge pressure is admitted to the control cylinder.

For a better understanding of the invention, reference may be had to the accompanying drawing in which Fig. 1 is a perspective view partly in section of a reciprocating compressor embodying the present invention, and

Figs. 2 and 3 are plan views illustrating preferred forms of discharge or intake valves for the compressor of Fig. 1.

Referring now to the drawing, the compressor as illustrated comprises a cylinder block 1 and an unloading compressor head 2 clamped together by suitable bolts or other devices (not shown) against a valve plate 3 which fits within circular seats 4 and 5 in the block and head respectively. A piston 6 is mounted for reciprocating movement within the cylinder, it being connected through a connecting rod (not shown) in the usual manner to a motor driven crank. The valve plate 3 is provided with a circular opening 7 concentric with the cylinder 1 and having its lower end of the same diameter as the bore of the cylinder, its upper end being shown tapered slightly inwardly. An annular exhaust port 8 is formed within the opening 7 by an annular member 9 forming part of a generally cylindrical member 10, the inner walls of which form the side walls of a control cylinder 11 within the compressor head 2.

The plate 3 is also provided with anannular intake port 12 opening into the cylinder by way of a conical recess at the side of the cylinder and formed by chamfering. the cylinder block about the upper end of the cylinder. The port 12 communicates with the outside of the compressor through a plurality of radial passages 15 opening about the periphery of the plate into an annular recess 16 of generally triangular cross section. The recess 16 is enclosed at its outer periphery by a band 18 provided with a plurality of perforations 19 through which suction gas is admitted to the recess 16 from within the hermetically sealed casing 20 surrounding the compressor assembly which assembly may comprise additional cylinders. A suction gas inlet 21 in the wall of the casing 20 provides entry for suction gas for example from the low pressure side of a refrigeration circuit.

The intake port 12 is closed by a flexible ring valve 22 constructed of spring material of a thickness which permits flexing of the inner periphery of the valve 22 away from the suction port 12 within the recess 14 to admit suction gas to the compressor cylinder during the downward stroke of the piston 6. During the discharge stroke of the piston 6, the compressed gas is exhausted through port 8 which is controlled by a flexible annular valve 23 free to flex conically between its position seated against the exhaust port 8 and a position against a back ing member 24 having a plurality of openings 25 through which the compressed gas passes into the annular exhaust gas chamber 26 within the heat 2 and from there to the discharge conduit 28. Preferably the valves. 22

3 and 23 have their outer periphery scahoped as indicated in Figs. 2 and 3 to reduce the stifiness thereof. In the case of the valv e plate 23 the scallops provide openings through which the gas may escape or pass from are exhaust port 8 through the openings 25 into the exhaust gas chamber 26. s

The inlet and exhaust valve structure is not part of the present invention, but it is rather described and claimed in the co-pendin'g application of Kenneth K. Cooper, Serial No. 287,747, filed May 14, 1952, and assigned to the same assignee as thejpresent invention. It is to be understood that the present invention is not limited to any particular inlet and exhaust porting arrangement or valve structure provided such structure is such that it is, compatible with the unloader head arrangement of the present invention which will now be described in detail. 7

The control cylinder 11 concentrically located in the head 2 above the compression cylinder 1 forms part of the unloading arrangement. It has an opening 30 at the lower end thereof communicating with the compressor cylinder 1, the inturned flange 31 surrounding this opening forming a valve seat 32. Slidably or reciprocably disposed within the control cylinder 11 is a differential piston 33 the lower end 34 of which is the smaller and forms a valve which seats on the valve seat 32 when the piston 33 is in its lowermost position.

The piston is held in this position during the normal operation of the compressor by 'high pressure discharge gas admitted to the cylinder 11 from the discharge or'exhaust conduit 28. Means foradinitting gas at discharge pressure to the cylinder 11 comprises a control tube 35, a three-way valve 36 and a conduit 37 connected to the discharge conduit 28. When the pressure within'the control cylinder 11 is equal to or approaches the discharge pressure from the cylinder 1 the piston 34 havingits larger piston element 38 subjected to this high pressure is held in its lowermost position against the pressure within the cylinder 1. Under these conditions the'compressor'operatesin a normal loaded manner withthecompressed gas being discharged from the cylinder through the valve 23 controlling the exhaust ports into the exhaust gas chamber 26 and from there through theexhaust or-discharge conduit 28.

Means for unloading the cylinder 1 comprisesan unloader port 40 in the head 2, one'end 41 of which communicates with the interior of the hermetically sealed casing 20 forming a reservoir for gas' at'suctiohpressure and member end 42 of which terminates in the lower portion of the cylinder 11 adjacent the valve seat '32. While onlyone-port is shown,it is to beunderstood that more than one can be employed'in'which case they are spaced about the cylinder 11. It will be seen that by'this arrangement when the differential piston is raised 'toits uppermostposition with the 'upper'pist'on element-38 en'- gaging the shoulders 43 provided at the upper end of the control cylinder 11, the unloading port or'ports 40 open to the interior of the compressorcylinder 1 placing cylinder 1 in direct communication withtheinterior of the casing 20.

Movement of the differential piston 33 in control cylinder 1 to its uppermostpositionis efiected fby venting the cylinder 11 to suction pressure. This isaccomplished by changing'thepos ition of the three-way valve 36 so that the control tube 35 is connected to the conduit 44 one end of which is connected to the valve 36 and the other end 'of which terminates within the casing 20. By lowering the pressure above the piston element 38 to a pressure approximating suction pressure, the pressure within the cylinder 1 will cause piston 33 tob'e pushed upwardly to the top of the cylinder 11 against shoulders 43.

While frictional forces between the differential piston 33 and the walls forming the control, cylinder 11 aid in or may be sufficient to hold the piston 33 in its uppermost 4 unloading position during unloaded operation of the compressor, any tendency for the piston to chatter while in this position can be eliminated by means of a dash pot 45 comprising the annular aperture formed by the cooperating sloping shoulders 46 and 47 respectively provided on the Walls of the control cylinder 11 and the piston 33. Oil is continuously furnished to the dash pot 45 by means of the 'oil tube 48 connected to the compressor oil pump (not shown). The cross-sectional area of the dash pot 45 will of course depend upon the position of the differential piston 33 within the control cylinder 11, it being considerably larger when the piston is in its uppermost position. The seal 50 provided between the upper and lower segments of the difierential piston 33 serves to confine the oil to the desired area surrounding the piston 33 and also forms a gas seal to prevent leakage of discharge pressure from the control cylinder 11 into the compressor cylinder 1 during normal operation of the compressor. The seal 50 is compressed between the upper piston element 38 and the lower piston element 34 by means of the bolt 51 securing these two elements together.

The three-way valve 36 is shown as being a solenoid controlled valve including solenoid 52 which when energized moves the valve 36 to a position connecting the control tube 35 to the discharge conduit 28. Energization of the solenoid 53 moves the valve 36 to a position venting the cylinder 11 through conduit 44 to suction pressure within the casing 20.

The control of valve 36 may be in response to any condition orchange of condition with reference to the operation of the compressor, the compressor driving means or the system such as a refrigeration system of which the compressor may form a part. In other words the solenoid coils 52 and 53 may form part of-any electrical control system designed to operate the compressor cylinder 1 in an unloaded condition under certain circumstances and in a loaded or normal condition under other circumstances. For example it is frequently desirable to unload one or more cylinders of a multi-cylinder compressor or one or more compressors driven by a common driving means in order to decrease the load on the driving means during starting of the compressor units. Alternatively the cylinder 1 may be loaded, or unloaded in order to control the capacity 'of a refrigeration system of which the compressor cylinder 1 forms a part. In such cases the valve 36 may be caused to operate in response to a change in suction pressure orin discharge pressure. It will also be obvious that'an electrical control system for the valve 36 is not required "as the valve, for example, could be directly operated by a'suitable bellows arrangement in response to a change inpressure within the systerm.

In the operation of a compressor cylinder provided with the unloader head of the present-invention, the piston 33 is normally held in the valve closing position by the introduction of discharge pressure from the dis charge conduit or a discharge gas reservoir into the cyl1n der '11 so that when the compressor is started the piston 6 within the compressor cylinder [in its downward motion draws 'gasinto the cylinderl through the battle strip 18 and the valve 12. As the piston rises in the cylinder the gasesare cornpressedand when the cylinder pressure is slightly higher than discharge pressurethe discharge valve 23 opens as'a result'of this increased pressure and the compressed gas flows through the discharge port 8 into the exhaust gasc amber26 from where it is piped oif through'the' exhaust or discharge conduit 28. On'the'other hand whenthe-control cylinder 11 is vented to suction pressure'orto'a lower pressure such that the differential piston33' is moved by the compression pressure 'within'the compressor cylinder 1 to its uppermost position against shoulders 43, both the intake valve 22 and the exhaust valve 23 are completely short fact that thegas at circuited or bypassed due to'the suction pressure within the casing 20 is repeatedly taken in and exhausted through the unloader port 40 during the reciprocating motion of the piston 6. Thusit will be seen that the valve losses are cut to a minimum by this unloading arrangement as it bypasses not only the discharge valve 23 but also the suction or intake valve 22.

So long as the control cylinder 11 is vented to suction pressure the difierential piston 33 will be maintained in its uppermost position by the oil pressure in the dash pot arrangement 45. The small static force imparted by the oil pressure in the dash pot 45 is not suflicient to open the valve against discharge pressure within the cylinder 11 but is suflicient to hold it in the unloaded position and prevent chatter during unloaded operation of the compressor. This slight oil pressure also cushions the unloading piston when it returns to its lowermost position after introduction of gas at discharge pressure into the control cylinder 11. As the pressure within the control cylinder 11 builds up the differential piston gradually moves downwardly forcing oil from the previously enlarged dash pot 45 back through the tube 48 to the oil pump system until the lower end thereof seats against the valve seat 32.

It has been found that the compressor cylinder provided with an unloader head of the present invention runs much cooler during operation in the unloaded condition than is the case with many unloading devices arranged for example in the discharge or exhaust line in the use of which gas is continuously discharged from the compressor under pressure and through the exhaust valve even operating under unloaded conditions.

While the invention has been illustrated in connection with a specific type of compressor, other applications will be readily apparent to those skilled in the art. It is not therefore desired that the invention be limited to the specific details illustrated, and it is intended by the appended claims to cover all modifications which fall within the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States Patent Oflice is:

1. A compressor comprising a compression cylinder and an unloading head including a control cylinder and an unloading port communicating with said compression cylinder, a differential piston in said control cylinder including valve means for closing said port, means for subjecting said piston to discharge pressure to maintain said port closing means in an operative position, said control cylinder and said differential piston comprising cooperating wall portions defining an annular chamber, and means for admitting a cushioning fluid to said chamber.

2. A compressor comprising a compression cylinder and an unloading head including a control cylinder and an unloading port communicating with said compression cylinder, a dilferential piston in said control cylinder including valve means for closing said port, means for subjecting said piston to discharge pressure to maintain said port closing means in an operative position, said control cylinder and said walls having cooperating inclined shoulder portions intermediate the ends of said piston defining an annular chamber, and means for supplying a fluid to said chamber to cushion the movement of said piston to its port closing position.

3. A compressor including a compressor cylinder and a cylinder head, said head comprising walls defining a control cylinder within said head, an unloader port opening into said compressor cylinder, a differential piston within said control cylinder for closing said port opening, the smaller end of said piston being subject to pressures within said compressor cylinder and means communicating with said control cylinder for subjecting the larger end of said piston to the discharge pressure of said cylinder to maintain said port opening closed, said control cylinder and said piston having inclined cooperating wall portions defining an annular chamber, and means for admitting a cushioning fluid under pressure to said chamber.

4. A gas compressor comprising a compressor cylinder, a hermetic casing surrounding said compressor, said compressor including asuction port opening into said casing and a discharge conduit for compressed gas, a cylinder head including walls defining a control cylinder above said compressor cylinder, an unloader port having one end communicating with said compressor cylinder and an outlet communicating with the interior of said casing, a differential piston in said control cylinder movable between a normal position closing said one end of said unloader port and an unloading position opening said one end, means communicating with said control cylinder for selectively subjecting the larger end of said differential piston to gas at compressordischarge pressure to maintain said piston in its normal position and to vent said cylinder to suction pressure for effecting movement of said diiferential piston to a position opening said unloader port, said control cylinder and said differential piston having cooperating wall portions defining an annular chamber, and means for supplying a cushioning fluid to said chamber.

5. A gas compressor assembly including a compressor cylinder having a suction conduit and a discharge conduit, a casing hermetically enclosing said compressor cylinder and forming a suction gas reservoir, said suction port communicating with said reservoir, a cylinder head including walls defining a control cylinder concentric with said compressor cylinder, said control cylinder having an opening at the lower end thereof communicating with said compressor cylinder, an unloader port in said head having one end communicating with said suction gas reservoir and the other end adjacent the lower end of said control cylinder, a differential piston disposed within said control cylinder, the lower and smaller end of said differential piston in its normal position closing said other end of said unloader port and said opening at the lower end'of said control cylinder and being subjected to pressures within said compressor cylinder, a control conduit including valve means for selectively admitting to said control cylinder above the upper end of said differential piston gas at discharge pressure from said discharge conduit to maintain said piston in its normal position against the pressures within said compressor cylinder and gas at suction pressure from said suction gaschamber to permit the pressure within said compressor cylinder to move said. piston to a position opening said unloader port to said compressor cylinder, said control cylinder and said piston.

having cooperating shoulder portions forming an annular chamber intermediate the ends of said piston and means: for admitting a cushioning fluid under pressure to saidfi chamber.

6. A gas compressor assembly including a compressor cylinder having a suction conduit and a discharge con-- duit, a casing hermetically enclosing said compressor cylinder and forming a suction gas chamber, said suction port communicating with said reservoir, a cylinder head including walls defining a control cylinder concentric with said compressor cylinder, said control cylinder having an opening at the lower end thereof communicating with said compressor cylinder, an unloader port in said head having one end communicating with said suction gas reservoir and the other end adjacent the lower end of said control cylinder, a diiferential piston disposed within said control cylinder, the lower and smaller end of said dilferential piston in its normal position closing said other end of said unloader ports and said opening at the lower end of said control cylinder and being subjected to pressures within said compressor cylinder, a control conduit including valve means for selectively admitting to said control cylinder above the upper end of said differential piston gas at discharge pressure from said discharge conduit to maintain said piston in its normal position against the pressures within said compressor cylinder and gas at suction pressure from said suction gas chamber to permit the pressure within said compressor cylinder to move said piston to a position unloading said compressor cylinder through said unloader ports, said control cylinder and said piston having cooperating inclined wall portions, defining an annular chamber intermediate the ends of said piston and means for admitting a fluid under pressure to said annular chamber to cushion said piston and to maintain said piston in its unloading position.

7. A gas compressor assembly including a compressor cylinder having a suction conduit and a discharge conduit, a casing hermetically enclosing said compressor cylinder and forming a suction gas chamber, said suction port communicating with said reservoir, a cylinder head including walls defining a control cylinder concentric with said compressor cylinder, said control cylinder having an opening at the lower end thereof communicating with said compressor cylinder, an unloader port in said head having one end communicating with said suction gas reservoir and an inlet adjacent the lower end of said control cylinder, a differential piston disposed within said control cylinder, the lower and smaller end of said differential piston in its normal position closing said other end of said unloader ports and said opening at the lower end of said control cylinder and being subjected to pressures within said compressor cylinder, a control conduit including valve means for selectively admitting to said control cylinder above the upper end of said differential piston gas at discharge pressure from said discharge conduit to maintain said piston in its normal position against the pressures within said compressor cylinder and gas at suction pressure from said suction gas chamber to permit the pressure within said compressor cylinder to move said piston to a position unloading said compressor cylinder through said unloader ports, said control cylinder and said piston having cooperating inclined wall portions forming an annular chamber intermediate the ends of said piston and means for admitting a fluid under pressure to said chamber to maintain said piston in its unloading position.

References Cited in the file of this patent UNITED STATES PATENTS 231,446 Presbray Aug. 24, 1880 831,522 Reardon Sept. 18, 1906 FOREIGN PATENTS 276,623 Great Britain Oct. 27, 1927 

